10 important things about the Emergency lighting maintenance factor
The maintenance factor is defined as the “ratio between the average luminance in the work plane after a certain period of use of a lighting installation and the initial average luminance obtained in the same conditions for the installation” taking into account all the losses, including maintenance of lamplight. A particularly significant example of this is the use of 0.8 as a maintenance factor for the luminaries (MF) when calculating the LED lighting specifications.
In fact, this has become something of an elephant in the lighting design room: the problem is there, and we all know it. But we still have to address this issue head-on. The maintenance factors refer to the fact that the lighting installations will gradually reduce the amount of light they provide for several years, due to the depreciation of light, dirt, faults, etc..The FM is a percentage of the total light output at the beginning of the installation’s life, to which the output may eventually fall. It tells you how much you need to increase the light level at the start, to stay above the required level during the life of the installation.
Therefore, if the level of light required during the life of the project is 500 lx, and the maintenance factor is set at 0.8 (or 80 percent), then to maintain the lighting at the required level, it must be installed 625 lx initials in space.
These are the 10 things that all lighting professionals need to know about maintenance factors:
- Maintenance factors are recognized as crucial by the industry:
The Lighting Code of the Light and Lighting Society states that: ‘The lighting scheme must be designed with a global maintenance factor calculated for the selected lighting equipment, the environment, and the specified maintenance program’.
- A maintenance factor of 0.8 is not adequate for each project:
Although 0.8 is a useful gold rule, it is an arbitrary figure, and there is no reason why it should be used in every lighting installation project. Each project is different, so the maintenance factor must be modified to adapt to the circumstances and the lighting technology used.
If we consider which are the key elements that intervene in the FM, then we see a series of factors that make up the final figure. The formula for the general maintenance factor for interior lighting is:
- LLMF: a factor of maintenance of the light of the lamp.
- LSF: lamp survival factor.
- LMF: maintenance factor of the luminaries.
- RMF: maintenance factor of the area.
- SMF: surface maintenance factor.
- The maintenance factor of the lamp light is particularly important for the LED:
Factors such as RMF and SMF are affected by the location of the luminaries, be it an industrial warehouse or an office, for example. This, in turn, would affect the LMF in terms of dust accumulation, which has an effect on light levels.
Pollution levels for the luminaries and space can be viewed in the same way for LEDs as for fluorescent lighting: dust and dirt will affect the output quality of both. However, with LED lighting, the LLMF is particularly important, and so is its impact on the overall maintenance factor.
LEDs have a very long lifespan; in fact, it is very likely that an office will be restored before it is necessary to replace the LED lighting.
- The useful life is key to the calculation in terms of energy use and cost:
When specifying LEDs, it is very important to indicate the useful life used in the calculations, since it will lead to decisions about the initial light level and the number of luminaries installed. This will greatly affect the amount of lighting required and, therefore, will have an impact on both capital and operating costs.
- The products can survive the scheme in which they are installed:
Having an accurate LLMF to find the correct maintenance factor for a lighting project has other benefits in terms of planning for the client’s requirements. For example, with these extended LED lifetimes available, customers can consider whether they need a life of 50,000 hours in their lighting system.
Why plan between 12 and 15 years of operation, if the customer is only accepting a seven-year lease for an office space? By changing this value, the LLMF will be altered, and the amount of light and the number of luminaries could be reduced considerably. This will save the client money in the short and long term.
- The “like” comparison is very important for designers and end users:
One of the main challenges for those who plan lighting installations is that it is difficult to compare when specified.
For example, we find office luminaries that can be L80 B10 50,000 hours at 25 ° C up to L70 B50 30,000 at 25 ° C. In addition, the lack of consistency in the comparative figures makes it difficult for customers to make a clear comparison.
- The new standards can help with comparisons:
Some very useful information sources have been developed for use throughout Europe to help Emergency lighting specialists find the correct figure quickly. One of them is the ENEC + organization that is developing standards for the validation of the useful life and performance of LED-based products.
The objective is to provide the users of the products with the confidence that what they are specifying and buying will work as indicated. The ENEC + brand will also standardize the use of L and B factors, making direct comparisons much easier.
Another organization that has carried out in-depth research in this field is ZVEI, a European body for the electrotechnical and lighting industries. It has produced a guide for reliable planning with LED lighting.
- Just because the FM is above 0.8 does not mean it’s wrong:
Customers are right to distrust the high numbers of maintenance factors. But just because it is higher than 0.8 does not do it badly.
Designers in the early stages of a project, whether it’s new construction or remodeling, often work without all the information. Some intelligent approaches are to be expected. However, with a standardized method to verify available LLMF and LSF, and also guidance on how to directly compare them, there is no reason to use 0.8 because it has always been done that way.
Too often, designs that use a precise maintenance factor of 0.88 can be returned with a request to use 0.8, although that is an incorrect figure. This encourages practice and must be stopped.
- Poor design and over-specification waste the benefits of LEDs:
As the SLL Code for Lighting states: ‘FM has a great impact on energy efficiency’. If we specify too much lighting at the beginning of a project due to inaccurate maintenance factors, then the customer will pay a lot for their electricity bills.
It has often been said that in the world of energy saving, lighting is the ‘easiest fruit’, could it be because it has been specified too much too often and for too long?
- We can all improve things:
Designers should stop applying 0.8 universally and treat each project as something unique. And customers should carefully observe lighting costs and clarify their requirements. The over specification is already a problem in other areas of construction services such as pumps and fans. It is not necessary that the lighting take the same route.